1,721,022 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Remediating small-scale migratory fish barriers with floating fish ramps
Get PDFInstream barriers are a well-documented stressor for diadromous fish species, and can be numerous and costly to remediate. In New Zealand, previous experiments have investigated the swimming ability of indigenous migratory fish over small ramps, but this work has not led to the development of cost-effective ramps that can be deployed by river managers. This study built on previous research and investigated the effect of ramp surface type on the swimming ability of two species of diadromous fish; inanga (Galaxias maculatus) a weak swimmer, and redfin bully (Gobiomorphus huttoni) a moderate climber, in an effort to inform the design of a floating plastic ramp that could be installed at low head instream barriers. Three phases of tank trials in the Hawke’s Bay tested different ramp substrates, including rock climbing holds, and small and large raised Miradrain® cusps. The results indicated that a linear arrangement of small cusps provided an optimal surface for swimming species such as inanga while redfin bully passage rates did not differ between the surfaces tested. The addition of spat rope reduced velocities and increased depth on all surfaces, and increased passage rates for inanga on ramps with large cusps, and redfin bullies on both cusp sizes. Fish surveys were conducted at 4 lowland streams in Hawke’s Bay in order to characterise fish communities, investigate the impact of barriers on their distribution, and evaluate the success of ramp installations in facilitating passage. Fish communities were impacted by barriers to varying degrees depending on the climbing ability of different species present. Inanga and redfin bully abundances were lower above the barriers, whereas eel abundances were similar between upstream and downstream reaches. Rotomoulded plastic floating ramps lined with small cusps were installed at barriers on 2 streams, the Awanui and the Irongate. Inanga were found above the barrier in the Awanui Stream 12 months after a ramp was installed, but fish did not pass over the wooden weir on the Irongate Stream. Buoyancy issues with the Irongate ramp are thought to have reduced its utility and potentially hindered fish passage. The buoyancy issues have since been overcome, and further monitoring is required to assess whether fish passage is consequently improved. These results show that floating rotomoulded ramps can be an effective and cost-effective tool for remediating small scale instream barriers to migratory fish.
Partitioning along reproductive niche dimensions in sympatric New Zealand freshwater bivalve species
Get PDFSympatric species of freshwater mussels in the order Unionida may need to partition resources to enable coexistence due to their relatively sedentary life-style and complex symbiotic life-phase dependent on host-fish. Although new data on their reproductive biology is being increasingly documented, particularly in the Northern Hemisphere, major gaps remain in New Zealand where two threatened Hyriidae, Echyridella aucklandica and E. menziesii, can co-occur. This thesis combines multiple approaches to elucidate the reproductive ecology of the previously unstudied E. aucklandica compared to the more widespread E. menziesii, and to examine mechanisms enabling their successful coexistence. I use field and laboratory investigations to compare reproductive niche parameters along three major resource use dimensions: host-fish species, reproductive phenology (time), and habitat use (space), and show that these two sympatric congeneric species have evolved sharply contrasting reproductive strategies.
Complex adaptations were identified among the two Echyridella species through contrasting use of larval (glochidia) host-fish infestation strategies and contrasting glochidia morphometry. Female E. aucklandica were found to produce conglutinates, mucus packages containing miniature glochidia thought to lure specific fish to them by resembling fish prey. This is thought to be one of the first Unionida species outside of North America reported to be using functional conglutinates to mimic host diet as an infestation strategy. Miniature glochidia produced by E. aucklandica were around three times smaller than those of E. menziesii, which along with other features such as shape and buoyancy, were consistent with morphological features found in host-specific unionid species elsewhere.
For the first time, the brooding phenology of E. aucklandica is reported, filling an important data gap on the basic biology of this poorly known and threatened species. Though E. aucklandica began brooding earlier and remained gravid for longer than E. menziesii, the brooding onset for both species generally occurred in winter (E. aucklandica in May–July, E. menziesii in August), reaching peak brooding (and thus glochidia release) in late austral spring to austral summer (November and December). High temporal overlap in glochidia development of these two species was observed, particularly during peak brooding when mature glochidia are expected to be released. Intra- and interspecific differences in reproductive timing identified key thermal cues (particularly accumulated degree days) associated with brooding onset and glochidia maturation in both species. The importance of water temperature suggests that changes in climatic conditions have the potential to cause negative effects on both species by causing mismatches between mussel reproduction and host phenology.
Field and laboratory studies of glochidia attachment and development on fish confirmed host specificity for E. aucklandica and host species partitioning between the two Echyridella species. Echyridella menziesii, was found to infest a wide range of fish species, being particularly prevalent on benthic Gobiomorphus species and Anguilla dieffenbachii, in contrast to E. aucklandica which produced viable juveniles only on the pelagic Retropinna retropinna. However, this Retropinnidae species was found only in low numbers across both study sites investigated and found to be infested with consistently low numbers of E. aucklandica glochidia, suggesting it may be a secondary rather than the primary host. Laboratory investigations confirmed that E. aucklandica’s miniature glochidia encysted exclusively on the gills of R. retropinna, in comparison to E. menziesii which attached not only on the gills but also externally on the fins and skin of its host. Miniaturised glochidia of E. aucklandica grew nearly five times their original size on R. retropinna before maturing as juveniles, compared to the larger E. menziesii glochidia which stayed the same size throughout metamorphosis. As a result, metamorphosis duration for E. aucklandica glochidia was significantly longer than for the larger E. menziesii, but only by two to three weeks.
Passive integrator transponder (PIT) tagging was used in a coastal Waikato stream in combination with electrofishing to track movements of both mussel species and determine host fish species locations within mapped habitats, to better understand spatial and temporal movement patterns of both sexes in relation to species-specific timing of fertilisation, glochidia release and host fish infestation. During the glochidia release season, results showed evidence of relatively high net horizontal movement rates and active bank-ward cluster formation in tagged individuals of both species. Spatial overlap between mussel species and their respective host fish was partially observed for E. menziesii, but could not be confirmed for the host-specific E. aucklandica due to only one R. retropinna being captured. Furthermore, vertical positions of mussels varied throughout the onset brooding period for both species, but generally, proportions of female mussels increased at the sediment surface during respective reproductive onsets. A moderate, bed-moving flood event that occurred during this experiment was associated with downstream displacement of both mussel species, with potential flood-flow refugia associated with riparian vegetation and debris in bank habitats apparently providing resistance to dislodgement.
This research provides critical information on the reproductive biology and partitioning of reproductive niche dimensions associated with the coexistence of sympatric E. aucklandica and E. menziesii. The findings will assist in the development of conservation strategies and stream management interventions to enhance freshwater mussel recruitment and survival in northern New Zealand streams
Sources and effects of catchment-derived bioavailable contaminants in Hamilton urban streams
No full textAwareness of the consistently degraded state of urban streams, with lower biodiversity has heightened worldwide, increasing restoration initiatives to ameliorate the adverse effects. The present study examined anthropogenically-derived contaminants in water and sediments and bioaccumulation in tissues and bile of shortfin eels (Anguilla australis) in Hamilton City urban gully streams. Bioassays were also conducted with two native Crustacea; the amphipod Paracorophium lucasi and freshwater crayfish (kōura) (Paranephrops planifrons) to test endpoints of survival, reburial behaviour and growth. Results of dissolved Cu, Pb and Zn showed the industrial Waitawhiriwhiri catchment, with higher impervious surfaces, to have the greatest potential for generating contaminants in stream waters. Relationships between sediment contaminant concentrations and upstream % impervious area suggest an association with stormwater runoff and metal accumulation. Shortfin eels from Gibbons Creek and Lake Rotoroa bioaccumulated high concentrations of Pb and As respectively in livers, and PAH metabolite pyrene-1-glucuronide in bile was found in many eels, highlighting the bioavailability of these contaminants. Muscle tissues cocnentrations of Pb and Hg in some sites triggered food safety guidelines presenting a low risk for human consumption. Amphipods exposed to sediments from Lake Rotoroa had significantly reduced survival compared with those exposed to other site sediments in a 10-day sediment toxicity test. Photo-induced toxicity is not of concern for biota exposed to these sediments. Sediments did not induce any sub-lethal effect on reburial behaviour. Growth rates of kōura fed Salix fragilis leaf material incubated in Hamilton streams were not significantly different, and the short duration of the study meant conclusions could not be made on the significance of observed accumulated metals and metalloids on differences in growth rates. Results of this study highlight a number of locations in the Hamilton stream network, where contaminants are of concern, especially in streams with fully urbanised catchments with high effective imperviousness and legacies of past land use or pollution. Bioavailability of some metals, metalloids and PAHs is constraining the diversity of some species present in these streams, although not apparent for shortfin eels, as they are very common
Quantifying relationships between kōura (Paranephrops planifrons) abundance and micro-habitat features in Waikato hill-country streams
Get PDFKōura (Paranephrops planifrons) is considered a taonga species by Māori and was once an abundant traditional fishery harvested throughout New Zealand. Kōura populations are under pressure in Waikato hill-country streams due to a range of factors including habitat loss and water quality degradation. Now that stakeholders have been engaging in collaborative decision-making and practices to restore/enhance biodiversity and ecosystem health within the Waikato catchment, there is opportunity to implement measures specifically targeted at kōura. Information on kōura habitat requirements to assist with the development of habitat enhancement work is therefore timely.
This research comprised two discrete studies which, in combination, provide important insights into daytime habitat use by kōura in Waikato hill-country streams. The first study was a field survey that examined in-stream habitat characteristics affecting kōura density and size, with a focus on juveniles ≤ 8 mm orbital carapace length (OCL), across a range of scales ranging from habitat patches to streams with contrasting catchment and riparian vegetation treatments – pasture, early or late riparian planting, and native forest. Micro-habitat variables related to kōura density included water depth and velocity, substrate size, and the area of bank undercuts and organic cover types, with root mat area significantly and positively related to juvenile densities across all scales. Although there was no significant effect of treatment type, there were strong associations between kōura and ponga logs, root systems, and coarse particulate organic matter (CPOM) across scales within and between streams.
The second study was a habitat manipulation experiment conducted to investigate whether kōura abundances, in particular juveniles, could be enhanced by additions of organic habitat consisting of 0.5 m² coconut fibre matting to simulate ponga (Cyathea dealbata) root systems that occur on the stream bank, and 1 m² ponga frond bundles to simulate the natural habitat structures formed in native forested areas. These two artificial habitats were compared with natural in-stream cobble habitats. Kōura and toi toi (Gobiomorphus spp.), both showed a preference for ponga frond habitats which were predicted to provide submerged habitat for more than 200 days. Although the coconut fibre matting was predicted to outlast ponga frond bundles by up to 107 days, it was more susceptible to sedimentation and did not provide adequate habitat for kōura due to its dense structure.
This study highlighted the influence of riparian treatments, hydrological processes, and inorganic and organic habitats on kōura populations. Information from this study can provide restoration managers with guidance on how to enhance in-stream and stream edge habitat suitability for kōura and can be used with existing mātauranga Māori, and western and community science, to determine suitable vegetation for riparian planting, assess what factors and drivers contribute to in-stream habitat availability and sustainability, and identify important habitat features that relate to kōura when conducting habitat restoration
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Effects of emergent structure on the abundance and size distribution of Trichoptera in Bay of Plenty hill country streams
Get PDFRestoration of streams is not limited to recreating structural habitat complexity, but also requires recolonisation of biota that had been excluded prior to restoration. Aquatic insects are a key component of a streams ecosystem, but often do not recolonise restored sites at expected rates. It is hypothesised that this is due to a lack of suitable habitat for the oviposition of certain groups, particularly the Trichopteran family Hydrobiosidae which is known to use emergent stones to access the stream bed for oviposition.
I investigated associations between Trichoptera groups with different oviposition strategies and emergent structure in the form of boulders in six Bay of Plenty stream sites. I compared abundances and size class distribution of Hydrobiosidae, Conoesucidae and Hydropsychidae at sites with and without emergent boulders. Results from that study suggest that the presence of oviposition structure was not linked to either the abundance or size distribution of Hydrobiosidae within the sites we examined where other factors such as degree of shade, water velocity and substrate size were key determinant of larval abundance. This first suggested that Hydrobiosidae may arrive in sites lacking emergent structure via alternative means.
Two potential pathways for the colonisation of Hydrobiosidae in reaches without emergent structure were subsequently identified and investigated: (i) access via the banks or emergent vegetation for oviposition; and/or (ii) Hydrobiosidae drift from upstream areas with suitable oviposition habitat.
A study on longitudinal patterns of Hydrobiosidae drift showed inconclusive results, with no significant changes in drift densities or larval size with distance downstream of emergent structure.
A study on the lateral distribution of Hydrobiosidae in a reach lacking emergent structure provided evidence that adults were utilising stream banks to access submerged oviposition habitat with higher numbers of smaller Hydrobiosidae found near the stream edges compared to within the channel. Findings from my study suggest that there should not be any constraints on the recolonisation of Hydrobiosidae within a restored reach as long as: (i) there is suitable oviposition habitat <2km upstream of a restored site; (ii) there is a source population of adults capable of reaching oviposition habitat within the targeted stream; (iii) the water quality is suitable for colonisation; and (iv) instream conditions such as shade, substrate size and water velocities are within the preferred ranges
Field and laboratory investigations of Echyridella menziesii (Unionida: Hyriidae) interactions with host fishes
Get PDFGlobally, the study of freshwater mussels has increased markedly in recent years, spurred on by recognition that many mussel populations are declining or are already extinct. The New Zealand freshwater mussel Echyridella menziesii (Unionida: Hyriidae) has a current threat classification of ‘At Risk, Declining’, in part reflecting disruption of recruitment on host fish. The life cycle of E. menziesii includes a parasitic stage in which the larvae (glochidia) must attach to a host fish to transform into the juvenile stage. However, no research has been conducted to understand whether fish develop immunity that limits infestation rates, and little is known about the spatial and temporal variations of mussel-host interactions in natural environments in New Zealand. This study therefore aimed to: i) determine whether multiple infestations of E. menziesii glochidia influenced the suitability of common bully (Gobiomorphus cotidianus) as a host; and ii) quantify fish host associations over the glochidial release period in three contrasting Waikato streams.
Common bully considered naïve to E. menziesii were infested with glochidia in the laboratory, and placed in individual, flow-through tanks (22oC) which were flushed every second day to measure glochidia detachment and juvenile excystment. Fishes were infested either one, two or three times, with ‘control’ fish infested for the first time in the second and third rounds. There were no differences in cumulative detachment rates of glochidia and no major reductions in metamorphosis success across multiple infestations.
Metamorphosis success rate across all infestation rounds was ≤30%, and was highest when initial glochidia viability was also high. The lack of detectable immunity in common bully, at least after three sequential infestations, is promising for the future conservation of E. menziesii as host-fish are likely to be repetitively infested with glochidia over the mussel spawning season in a natural setting.
Infestation by glochidia was determined on the associated fish community, caught using a combination of electrofishing and minnow trapping. In parallel with these evaluations, mussel brood pouch development was assessed fortnightly from October 2018 to February 2019 at three Waikato stream sites. Peak glochidia release occurred in February when average monthly water temperatures were >18.8oC. A field method was developed to quantify glochidial attachment on external surfaces of fish, while internal attachment (gills, mouth) was quantified by laboratory dissection. While a range of fish hosts were identified, 86% of recorded glochidia were attached to Gobiomorphus species, including redfin bully (G. huttoni) and common/Crans bully (G. cotidianus/G. basalis). Most externally-attached glochidia (73%) occurred on caudal, pelvic and pectoral fins. Host associations appeared to favour benthic rather than pelagic species, and did not change throughout the mussel reproductive season despite seasonal change in fish communities.
This research demonstrates that common bully, and more broadly Gobiomorphus species, are important hosts for glochidia and do not develop immunity to repeated infestations. Gobiomorphus species have the potential to be very useful ‘tools’ to assist in restoring E. menziesii populations, and therefore conservation management must consider these host fish populations as well as other habitat and water quality factors affecting E. menziesii
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